This invention relates to an apparatus and method for enhancing heat transfer in a heat exchanger.
Heat transfer between a fluid flowing along a heat exchanger surface is confined primarily to a layer of the fluid in contact with the surface of the heat exchanger. Fin structures extending from the heat exchanger surface and contacting the fluid have been used by others to set up a flow disturbance which prevents this stratifying or laminar flow of the fluid flowing against the heat exchanger surface. The fins typically are formed to contact the heat exchanger surface and provide higher conductive heat transfer from the fluid to the surface.
In the case of fluid flowing in heat exchanger tubes, it is well known to use inserts to provide a turbulent flow of the fluid against the inside surface of the tube. Such tube inserts for producing turbulence are often called turbulators. The turbulator in the tube improves heat transfer, primarily by slowing down the velocity of the fluid flowing through the central portion of the tube or pipe cross section, and further improves the temperature distribution of the fluid in the cross section of the tube or pipe by conduction and mixing.
In heat transfer applications at high temperatures, radiative heat transfer takes on a dominant influence over convection and conductive heat transfer. Previous attempts have been made to take advantage of the higher radiation heat transfer by providing reradiant inserts, e.g., such as in flue gas recuperators. One such reradiant insert is disclosed in Kardas et al, U.S. Pat. No. 3,886,976. The Kardas insert uses a floating extended surface, i.e., an additional area accepting heat by convection and radiation from the hot gas, not integrally connected with the original heat receiving surface. Heat then is retransmitted to the original surface by the continuous spectrum of Stefan-Boltzmann radiation. Radial mixing and large effective radiating area can be obtained by using multileaf reradiators of the type shown in the Kardas patent in FIG. 5.
The aforementioned turbulators are designed for lower temperature operation and, for that reason, do not produce the most efficient heat exchanger insert at higher temperatures.
It is an object of the present invention to provide heat exchanger apparatus and method for enhancing heat exchange between a fluid and a heat exchanger surface, e.g., such as a heat exchanger tube.
It is another object of the present invention to provide heat exchanger apparatus and method of enhanced efficiency at higher temperature differences between the fluid and heat exchanger surface.
It is yet another object of the present invention to provide heat exchanger apparatus and method of enhanced efficiency at higher flow rates and pressure drops through a tubular heat exchanger.